Conventional fluid actuated vehicle braking systems include a source of fluid under pressure such as a compressor driven by the vehicle prime mover and connected to and building pressure in a fluid tank. The tank is connected by a main serviceline to the brake mechanism, the line including valve means actuated by the vehicle driver such as by operating a vehicle brake pedal. The service line includes means which on release of the pedal cause the line to be exhausted to atmosphere where the fluid is gas e.g. air or into a low pressure zone in the case of the fluid being a liquid i.e. oil.
Many conventional circuits include a second service line known as an emergency line which is supplied with pressurised fluid from a secondary pressurised fluid tank. Systems involving main and emergency service lines are known as two-line systems and are compulsory in many countries.
Three line systems are sometimes employed and in some countries are obligatory. In such systems a third service line, sometimes called a "dead man line" is included which line is actuated by action by the vehicle driver as by application of the vehicle hand brake by the driver, and operable if the main and emergency circuits are inactive or fail.
When a driver reverses a vehicle, particularly a large heavily laden goods carrying vehicle, his rear vision is often obstructed and he is unable to see an obstacle behind his vehicle. Rigid obstacles such as a loading bay or a wall may be damaged and also cause damage to the vehicle and where the obstacle is a human or animal body serious injury or death may result.
Detector devices are known which actuate a warning such as a horn or light in the driver's cab to alert the driver to apply the brakes but these suffer from the disadvantage that the driver's reaction time may be too long for a collision to be avoided. Also when the obstacle struck has moved out of contact with the detector it then ceases to activate the warning device.
It has also been proposed to provide detector devices at the rear of a vehicle or trailer which are connected into the brake circuit to apply the brakes.
One example of such prior proposal, is U.S. Pat. No. 2,588,815 Fasolino. This specification discloses a system for use with air brakes in which a detector bar is associated with switch means and a gear lever is also associated with switch means whereby a solenoid valve is operated when both switch means are also operated. The solenoid valve opens a fluid valve which is in a simple by-pass circuit of the foot brake valve to apply the brakes when both switch means are actuated. Fasolino does not, however, describe a practical system. In particular, there is no indication of the manner in which the brakes are released as the solenoid valve merely opens and closes an air line between the air tank and the brakes and there is no provision for releasing the air from the brakes.
Similarly U.K. specification No. 1,470,129 describes a valve in a foot brake valve by-pass circuit which is operated by a switch associated with a detector bar and a switch associated with a gear lever. The arrangement described is however completely impractical as is the Fasolino proposal.
An object of the present invention is to provide a vehicle reversing brake system in which the aforesaid disadvantages are minimised or eliminated.
A further object of the present invention is to provide a vehicle reversing brake system in which the braking action is such as to distinquish between contact with relatively rigid objects and contact with movable objects.
According to one aspect of the present invention we provide a vehicle braking system comprising fluid actuated brakes, at least one source of pressurised fluid, at least one service fluid line connected to said source of pressurised fluid, said braking system being arranged and adapted to apply the brakes in response to a change in pressure in said service line, the improvement which comprises the addition of an auxiliary braking system comprising:
(a) an auxiliary fluid circuit including a fluid control valve; PA0 (b) a detector mounted at the rear of the vehicle and movable between operative and inoperative positions; PA0 (c) first control means responsive to the position of the detector to act on said fluid control valve to cause it to provide an open fluid path in said auxiliary fluid circuit when the detector is in its operative position and to obstruct said fluid path when the detector is in its inoperative position; PA0 (d) second control means independent of said first control valve and responsive to the position a drive-controlled reverse selector on the vehicle, said second control means being arranged to insure that the fluid path in said fluid circut is open only when said driver-controlled reverse selector is in a vehicle-reversing condition; PA0 (e) said auxiliary circuit fluid control valve being so connected in said service line that upon operation of said fluid control valve, the fluid path in the service line between said valve and said source of pressurised fluid is obstructed and the fluid path between said valve and said brakes is opened. PA0 (a) an auxiliary fluid circuit including a fluid control valve; PA0 (b) a detector mounted at the rear of the vehicle and movable between operative and inoperative positions; PA0 (c) first control means responsive to the position of the detector to act on said fluid control valve to cause it to provide an open fluid path in said auxiliary fluid circuit when the detector is in its operative position and to obstruct said fluid path when the detector is in its inoperative position; PA0 (d) second control means independent of said first control means and responsive to the position of a driver-controlled reverse selector on the vehicle, said second control means being arranged to insure that the fluid path in said fluid circuit is open only when said drive-controlled reverse selector is in a vehicle-reversing condition; PA0 (e) said auxiliary circuit fluid control valve being so connected in said service line that upon operation of said fluid control valve, the fluid path in the service line between said valve and said source of pressurised fluid is obstructed and the fluid path between said valve and said brakes is opened; and PA0 (f) said auxiliary fluid circuit being arranged to be vented to atmosphere only when said first and second control means both are in a condition to cause an open fluid path in said auxiliary circuit.
According to another aspect of the present invention we provide a vehicle braking system comprising fluid actuated brakes, at least one source of pressurised fluid, at least one service fluid line connected to said source of pressurised fluid, said braking system being arranged and adapted to apply the brakes in response to a change in pressure in said service line, the improvement which comprises the addition of an auxiliary braking system comprising:
In this specification the expressions "fluid service line" refers to one of the fluid lines present in the conventional braking system, e.g. the principal service brake line operated by the driver's foot brake and the emergency line in a two-line system. In a three-line system it includes the additional emergency line known as the "dead man line".